Christmas shopping fever has gripped London with retailers in the capital's West End ringing up £150m in a weekend spending spree.

Hundreds of thousands of shoppers trooped to central London on Saturday and Sunday, according to the New West End Company, with shopper numbers up 16.5% on the same weekend last year. Crowds were boosted by an influx of visitors from Spain, Italy and Portugal, where the Feast of the Immaculate Conception holiday provided the window for a Christmas shopping trip to London.

Fortnum & Mason chief executive Ewan Venters said the 300-year-old Piccadilly store had its biggest ever Saturday, with sales up 13% on last year. "It was extraordinary. We could not have fitted a single extra person in the building," he said.

In December monthly retail sales nearly double to £39bn, and for store groups such as HMV, Argos and Dixons it is when they make the bulk of their profits. But with the tough economic conditions forcing Britons to rein in their spending, retailers are worried about the outlook for this year.

Hopes of a successful trading period for the industry have also been stoked by strong figures from John Lewis, which said that last week sales surged 15% to £142m, setting a new record for the department store chain. The retailer said the cold snap had lifted fashion sales, with coats, scarves and knitwear on shoppers' radar, and that gifts such as cashmere, lingerie and jewellery were in demand.